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Questions and Answers
Tetanus results in a sustained muscle contraction due to a decrease in intracellular calcium levels.
False
Motor units consist of a single α motor neurone and all the muscle fibers it innervates.
True
During sustained muscle contraction, all motor units are always active to prevent fatigue.
False
The optimal resting length of a sarcomere allows for maximum strength of contraction.
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Recruitment of motor units allows for graded increases in force during muscle contraction.
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Tetanus occurs only at low levels of stimulation and requires minimal action potentials.
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As muscle length increases, tension developed increases indefinitely.
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Smaller motor units are typically recruited last during muscle contractions requiring increased strength.
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The mechanism of contraction for smooth muscle is fundamentally different from that of cardiac muscle.
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A simple muscle twitch involves a contraction followed by sustained tension.
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Study Notes
Muscle Components
- Remember the individual components of a muscle fiber.
Muscle Fiber Length and Force
- The force a muscle generates when it contracts is related to its resting length.
- There is an optimal resting length for a sarcomere to achieve maximum strength of contraction.
- The "Length-Tension Curve" illustrates this relationship:
- As muscle length increases, tension also increases up to a limit.
- An overstretched sarcomere with no overlap between actin and myosin results in minimal force generation.
Muscle Contraction Strength
- Two factors can alter the force/strength of skeletal muscle contraction:
- Tetanus/Tetany
- Recruitment of Motor Units
Muscle Twitch
- A simple muscle twitch consists of a contraction followed by relaxation.
Tetanus in Skeletal Muscle
- Tetanus/Tetany is a sustained muscle contraction.
- At high levels of stimulation, repeated action potentials lead to a sustained rise in intracellular calcium.
- This sustained increase in calcium allows for greater contraction force than a single twitch.
Motor Units
- A motor unit consists of a single alpha motor neuron and all the muscle fibers it innervates.
- Motor units vary in size:
- Larger motor units provide less precise control.
- Smaller motor units provide fine control and are recruited first for smaller movements.
- To increase force, more motor units are recruited.
- During prolonged activity, motor units rotate so that some are contracting while others rest, delaying fatigue.
Cardiac Muscle Action Potential
- The cardiac muscle action potential is crucial for muscle contraction.
Cardiac Muscle Contraction Mechanism
- The mechanism of contraction in cardiac muscle involves a sequence of events triggered by the action potential, including calcium release and the sliding filament mechanism.
Smooth Muscle Contraction Mechanism
- Smooth muscle contraction operates via a different mechanism involving calcium signaling, but without striations or sarcomeres.
Muscle Types: Key Differences
- Smooth, cardiac, and skeletal muscles differ in:
- Structure
- Contraction mechanism
- Control
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Description
Test your knowledge on muscle components, length-tension relationships, and factors affecting muscle contraction strength. This quiz covers essential concepts about muscle fibers, contraction mechanisms, and the effects of tetanus and motor unit recruitment.
